So sorry to hear what you're going through right now. I raised my daughter by myself since she was 3. Reason sounds very familiar. The mother decided she was going to date a drug dealer. The rest is history. I also had to make several sacrifices since I didn't get any child support with her mom ending up in prison 3 different times.
My daughter was also diagnosed with Type 1 Diabetes right after her mom left. Had no insurance to help pay for her insulin, doctor visits, hospital stays. It was a very tough time in my life, and for my daughter. I never dated while I was raising her. Not until she graduated did I start dating.
I had one bad year out of my daughter at about the age of 12. She was starting to go through that independence phase. I somehow became the evil father overnight because I wouldn't let her roam the streets, or go to the mall with her friends without a parent being there also.
Once she started high school at Paschal, she realized just how much "Daddy" really did have her back, and I somehow became the "Cool Dad" to all of her friends. They would come to talk to me because they couldn't talk to their parents like that could me. I was the "Best Dad"again.
Try your hardest not to take it personal, and believe me, that isn't easy. They go through situations and/or phases in their life. The best advice I can give is pay close attention to things, changes, and especially her friends. Keep a very open line of communication for her to be able to come to you with ANYTHING. Don't try to be her best friend. They have enough friends, they don't need another. They need a PARENT to guide them, not a hangout buddy.
I don't know if anything I said helps, but if you have any questions, please feel free to reach out to me or even my daughter.